The present invention relates to wearable lenses, and more particularly, the invention relates to multifocal wearable lenses having reduced distortion.
Progressive lenses are lenses typically used in eyeglasses to assist wearers who have difficulty with accommodation. The lenses are typically divided into upper and lower portions, wherein the upper portion is designed to improve long-distance vision, and the lower portion is designed to improve intermediate and short distance vision. The lower portion of a progressive lens, the progressive portion, generally comprises a gradually reducing focal length relative to the upper, long-distance portion.
A common problem with progressive lenses is that the vision through the sides of the progressive portion of the lens is distorted, and can cause discomfort and headaches for the wearer. The distortion can cause discomfort for the wearer of the lens, particularly when the wearer moves and the wearer senses the kinetic distortion.
Several types of lens have been devised with the intention of minimizing the problem of distortion.
U.S. Pat. No. 5,455,642 (Kato) discloses a progressive lens having a radius of curvature that varies along the vertical direction. While Kato discloses that the lens provides a wider field of view for astigmatism, relative to lenses of the prior art, the two lower areas of distortion remain a problem for the wearer of the lens.
U.S. Pat. No. 4,426,139 (van Ligten) discloses a progressive lens with a near vision portion, an intermediate vision portion and a far vision portion, employing a cosine function in determining the lens curvature in the transition corridor between the far and near vision portions, so as to reduce the distortion in the peripheral area of the lens.
However there still exists an ongoing need for a lens construction that provides the wearer with an undistorted view through regions of the lens corresponding generally to the wearer""s peripheral vision.
In a first aspect, the present invention provides a multifocal ophthalmic lens having a distance optical center, comprising a first portion having focal properties, said first focal properties being substantially constant throughout said first portion; and a second portion having second focal properties extending downwardly from a location adjacent the distance optical center and having a focal length that varies progressively downwardly in said second portion; and two regions on either side of said second portion, each of said regions having focal properties selected to avoid optical distortion.
The regions, on either side of the second portion, are in conventional lens regions of visual discomfort due to varying focal properties leading to distortion. In the present invention these regions have constant focal properties and these can be one of: the same as the first portion; and different from the first portion. It is preferred for these two regions to have constant focal properties.
In a further aspect, the invention relates to a method of construction of lenses for a wearer with a field of view without regions of potential visual discomfort, wherein the method comprises the steps of:
constructing a long-distance lens piece;
constructing a progressive lens piece that mates with the first lens piece along peripheral edges of both lens pieces;
mating the lens pieces such that the progressive lens piece is substantially outside the regions of potential visual discomfort.
Preferably this technique is used simply to produce a master lens, for creating a mold, with final, production lens being molded in one piece.